The invention relates to antisense oligodeoxynucleotides against VR1, to corresponding nucleotide constructs, to cells, pharmaceutical preparations and diagnostic preparations containing these, to the use thereof in pain therapy and to methods for diagnosing symptoms associated with VR1 and for identifying pain-modulating substances.
The effective treatment of pain is a major challenge to molecular medicine. Acute and transient pain is an important bodily signal protecting people from severe injury by their environment or by overloading their body. In contrast, chronic pain, which lasts longer than the cause of the pain and the anticipated time frame for cure, has no known biological function and affects hundreds of millions of people worldwide. In the Federal Republic of Germany alone, some 7.5 million people suffer from chronic pain. Unfortunately, pharmacological treatment of chronic pain is still unsatisfactory and thus remains a challenge to current medical research. Currently existing analgesics often have an inadequate action and sometimes have severe side effects.
The search is thus now on for new targets or endogenous body structures which appear to provide a way of exerting pain-modulating action, for example using low molecular weight active substances or other compounds such as antisense oligodeoxynucleotides (ODN), in particular for the treatment of chronic pain.
The vanilloid receptor subtype 1 (VR1, also known as the capsaicin receptor) cloned by Caterina et al. (1997) is a promising starting point for the development of new analgesic drugs. This receptor is a cation channel which is predominantly expressed by primary sensory neurons (Catarina et al. 1997). VR1 is activated by capsaicin, a component of chillies, heat (>43° C.) and a low pH as a result of tissue injury, and brings about a calcium influx in primary afferents. VR1 knockout mice did not develop thermal hyperalgesia after tissue injury or inflammation (Caterina et al., 2000; Davis et al., 2000).
Antisense oligodeoxynucleotides, ribozymes and other catalytic nucleic acids may be used for the treatment, in particular of chronic pain, by degrading or modifying the mRNA of selected targets, in the case of the present invention the above-described VR1, to down-regulate the expression thereof and thus reduce the number of receptors per cell. The ODN attach themselves to the mRNA, so firstly blocking translation and secondly initiating degradation of the mRNA by RNase H, which cleaves the DNA/RNA duplex. Porreca et al. (1999) were able to demonstrate that intrathecally administered ODNs against the PN3/SNS channel in rats prevent the development of hyperalgesia and allodynia due to chronic nerve or tissue damage.
Even once the sequence of VR1 is known, effective blocking and cleavage of the mRNA in particular depends upon the selection of the correct antisense oligodeoxynucleotides, ribozymes and other catalytic nucleic acids. The target's mRNA is usually folded and only a few sites are accessible for attachment and subsequent cleavage. Nothing is known in the prior art about how to select the ODN correctly.